Heretofore, an acceleration sensor system used for an air bag safety system generally comprises an acceleration a sensor device generating an electric signal responsive to variation of an applied acceleration force and a circuit which amplifies and integrates an output signal of the acceleration sensor device. The system actuates an air bag when the an integrated value exceeds a predetermined value. Abnormal operation of the acceleration sensor system directly concerns human life, therefore an operation check of the acceleration sensor system is inevitable. An Acceleration sensor system having a self checking circuit for operation check is disclosed in U.S. Pat. No. 3,911,391. In this prior art, with the ignition switch ON in the vehicle, the system operation is checked. Concretely, a pulses generating circuit continuously generates two kinds of check pulses of different levels in response to ignition switch ON of a vehicle. An integrator integrates the output value of a piezoelectric sensor system for these pulses and a comparator compares each of the integrated results corresponding to the check pulses with a predetermined value. Level of the check pulses are set, if the sensor system operates normally, to exceed and not to exceed the predetermined value, respectively. In this prior art, an ignition element of the air bag is isolated during the checking to avoid actuating the air bag by the check pulse and if the checking result is normal, the ignition element is electrically connected to the sensor system. Therefore, this system can not make a check after the vehicle starts moving.